Effects Of Nitrogen And Nighttime Low Temperature On Photosynthetic Characteristics Of Davidia Involucrate Seedlings

Davidia involucrate is an endangered species, which is unique and rare in China. Due to the high economic and ornamental value,it is First-Grade State Protection species. It is a well-known greening tree species worldwide and has been introduced to Europe, America and other countries.D. involucrate is now in danger of extinction because of its special ecological characteristics, habitat destruction or some other reasons.The main problem for there searchers is how to protect them effectively by in situ conservation and overcome the adverse climate conditions in ex-situ conservation.In this paper, we used the method of control variable and took some potted D. involucrate seedlings as test objects.We used Li-6400 to determine the photosynthetic parameters and light response parameters of seedlings in continuous night time low temperatures.Also, we explored the contribution of nitrogen on photosynthesis and cold tolerance of the seedlings.Our aim was to reveal the response of D. involucrate seedlings in northern nighttime low temperatures during the growing season,and to study on the possibility of cold acclimation of seedlings. So that we would be able to know the approaches to increase cold tolerance of D. involucrate.Processed and analyzed by the test results, we got the following results and main conclusions:1. Night continuous low temperature produced a significant inhibition on photosynthetic characteristics and chlorophyll content of D. involucrate seedlings.When the conditions temperature was higher than 4℃, there would be a possibility of cold acclimation of D. involucrate Seedlings. If given a reasonable hypothermia induced treatment, D. involucrate seedlings would be likely to overcome the adverse effects of low temperatures in growing season.2. The effect of nitrogen on photosynthesis of D. involucrate is positive.It turns out to be very important to consider the form of nitrogen element, and using ammonium nitrogen only has no effects on the content of chlorophyll seedlings.There is no significant difference between the effects of the amount of fertilizer.Moreover, the type and proportion of nitrogen need to be further considered.3. Applied nitrogen fertilizer did not help to improve the cold tolerance of D. involucrate seedlings. The contribution of nitrogen was only on the adaptation speed of hypothermia.On the contrary, photosynthesis and chlorophyll content decreased with a small amount of nitrogen at low temperatures.In addition to the stomatal conductance, other indicators were not affected by the low temperature and nitrogen inter actions Generally speaking, applying nitrogen fertilizer is helpful on seedlings’ cold tolerance, but this was failed to find in this study.The reason for this was supposed to be that the nitrogen D. involucrate seedlings needed was not only in forms of amino group but also nitro group, which requires further study.